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</pre><pre class="rust ">
<span class="comment">// Pulled from std::char until encode_utf8 stabilizes. ---AG</span>

<span class="comment">// UTF-8 ranges and tags for encoding characters</span>
<span class="kw">const</span> <span class="ident">TAG_CONT</span>: <span class="ident">u8</span>    <span class="op">=</span> <span class="number">0b1000_0000</span>;
<span class="kw">const</span> <span class="ident">TAG_TWO_B</span>: <span class="ident">u8</span>   <span class="op">=</span> <span class="number">0b1100_0000</span>;
<span class="kw">const</span> <span class="ident">TAG_THREE_B</span>: <span class="ident">u8</span> <span class="op">=</span> <span class="number">0b1110_0000</span>;
<span class="kw">const</span> <span class="ident">TAG_FOUR_B</span>: <span class="ident">u8</span>  <span class="op">=</span> <span class="number">0b1111_0000</span>;
<span class="kw">const</span> <span class="ident">MAX_ONE_B</span>: <span class="ident">u32</span>   <span class="op">=</span>     <span class="number">0x80</span>;
<span class="kw">const</span> <span class="ident">MAX_TWO_B</span>: <span class="ident">u32</span>   <span class="op">=</span>    <span class="number">0x800</span>;
<span class="kw">const</span> <span class="ident">MAX_THREE_B</span>: <span class="ident">u32</span> <span class="op">=</span>  <span class="number">0x10000</span>;

<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">encode_utf8</span>(<span class="ident">character</span>: <span class="ident">char</span>, <span class="ident">dst</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> [<span class="ident">u8</span>]) <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span> {
    <span class="kw">let</span> <span class="ident">code</span> <span class="op">=</span> <span class="ident">character</span> <span class="kw">as</span> <span class="ident">u32</span>;
    <span class="kw">if</span> <span class="ident">code</span> <span class="op">&lt;</span> <span class="ident">MAX_ONE_B</span> <span class="op">&amp;&amp;</span> <span class="op">!</span><span class="ident">dst</span>.<span class="ident">is_empty</span>() {
        <span class="ident">dst</span>[<span class="number">0</span>] <span class="op">=</span> <span class="ident">code</span> <span class="kw">as</span> <span class="ident">u8</span>;
        <span class="prelude-val">Some</span>(<span class="number">1</span>)
    } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">code</span> <span class="op">&lt;</span> <span class="ident">MAX_TWO_B</span> <span class="op">&amp;&amp;</span> <span class="ident">dst</span>.<span class="ident">len</span>() <span class="op">&gt;=</span> <span class="number">2</span> {
        <span class="ident">dst</span>[<span class="number">0</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span> <span class="number">6</span> <span class="op">&amp;</span> <span class="number">0x1F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_TWO_B</span>;
        <span class="ident">dst</span>[<span class="number">1</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="prelude-val">Some</span>(<span class="number">2</span>)
    } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">code</span> <span class="op">&lt;</span> <span class="ident">MAX_THREE_B</span> <span class="op">&amp;&amp;</span> <span class="ident">dst</span>.<span class="ident">len</span>() <span class="op">&gt;=</span> <span class="number">3</span>  {
        <span class="ident">dst</span>[<span class="number">0</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span> <span class="number">12</span> <span class="op">&amp;</span> <span class="number">0x0F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_THREE_B</span>;
        <span class="ident">dst</span>[<span class="number">1</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span>  <span class="number">6</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="ident">dst</span>[<span class="number">2</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="prelude-val">Some</span>(<span class="number">3</span>)
    } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">dst</span>.<span class="ident">len</span>() <span class="op">&gt;=</span> <span class="number">4</span> {
        <span class="ident">dst</span>[<span class="number">0</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span> <span class="number">18</span> <span class="op">&amp;</span> <span class="number">0x07</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_FOUR_B</span>;
        <span class="ident">dst</span>[<span class="number">1</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span> <span class="number">12</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="ident">dst</span>[<span class="number">2</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&gt;&gt;</span>  <span class="number">6</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="ident">dst</span>[<span class="number">3</span>] <span class="op">=</span> (<span class="ident">code</span> <span class="op">&amp;</span> <span class="number">0x3F</span>) <span class="kw">as</span> <span class="ident">u8</span> <span class="op">|</span> <span class="ident">TAG_CONT</span>;
        <span class="prelude-val">Some</span>(<span class="number">4</span>)
    } <span class="kw">else</span> {
        <span class="prelude-val">None</span>
    }
}
</pre>
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